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""" |
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ETLT |
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Copyright 2016 Set Based IT Consultancy |
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Licence MIT |
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""" |
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import abc |
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class RegularDimension(metaclass=abc.ABCMeta): |
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""" |
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Abstract parent class for translating natural key to a technical key of a regular dimension. |
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""" |
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# ------------------------------------------------------------------------------------------------------------------ |
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def __init__(self): |
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""" |
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Object constructor. |
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""" |
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self._map = {} |
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""" |
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The map from natural keys to a technical keys. |
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:type: dict[T, int|None] |
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""" |
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# Pre-load look up data in to the map. |
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self.pre_load_data() |
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# ------------------------------------------------------------------------------------------------------------------ |
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def get_id(self, natural_key, enhancement=None): |
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""" |
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Returns the technical ID for a natural key or None if the given natural key is not valid. |
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:param T natural_key: The natural key. |
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:param T enhancement: Enhancement data of the dimension row. |
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:rtype: int|None |
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""" |
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# If the natural key is known return the technical ID immediately. |
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if natural_key in self._map: |
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return self._map[natural_key] |
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# The natural key is not in the map of this dimension. Call a stored procedure for translating the natural key |
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# to a technical key. |
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self.pre_call_stored_procedure() |
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success = False |
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try: |
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key = self.call_stored_procedure(natural_key, enhancement) |
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success = True |
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finally: |
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self.post_call_stored_procedure(success) |
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# Add the translation for natural key to technical ID to the map. |
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self._map[natural_key] = key |
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return key |
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# ------------------------------------------------------------------------------------------------------------------ |
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@abc.abstractmethod |
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def call_stored_procedure(self, natural_key, enhancement): |
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""" |
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Calls a stored procedure for getting the technical key of a natural key. Returns the technical ID or None if |
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the given natural key is not valid. |
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:param T natural_key: The natural key. |
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:param T enhancement: Enhancement data of the dimension row. |
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:rtype: int|None |
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""" |
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raise NotImplementedError() |
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# ------------------------------------------------------------------------------------------------------------------ |
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def pre_load_data(self): |
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""" |
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Can be overridden to pre-load lookup data from a dimension table. |
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:rtype: None |
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""" |
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pass |
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# ------------------------------------------------------------------------------------------------------------------ |
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def pre_call_stored_procedure(self): |
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""" |
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This method is invoked before call the stored procedure for getting the technical key of a natural key. |
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In a concurrent environment override this method to acquire a lock on the dimension or dimension hierarchy. |
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:rtype: None |
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""" |
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pass |
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# ------------------------------------------------------------------------------------------------------------------ |
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def post_call_stored_procedure(self, success): |
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""" |
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This method is invoked after calling the stored procedure for getting the technical key of a natural key. |
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In a concurrent environment override this method to release a lock on the dimension or dimension hierarchy and |
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to commit or rollback the transaction. |
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:param bool success: If True the stored procedure is executed successfully. If an exception has occurred. |
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:rtype: None |
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""" |
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pass |
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# ---------------------------------------------------------------------------------------------------------------------- |
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PyETLT /
etlt
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